The basic components of a fluorescent lamp or fixture are the tubes, ballast wires and lamp holders. The ballast controls the voltage and current to run the tube and provide it with enough power to light the lamp. The ballast is also designed to prevent electrical shock by limiting the current that can flow through the lamp and the tube.
The lamp contains a glass tube which is filled with mercury and inert gases (argon or krypton) at low pressure. Inside, there are two electrodes or filaments which are coated with phosphor that emits visible light when excited by ultra-violet radiation.
Fluorescent lamps are commonly used in commercial and industrial applications, as well as in residential and office lighting. They produce a much cooler color than incandescent bulbs and have a longer life span.
They are more energy efficient than incandescents and require less maintenance. They are usually rated at a lower current and can be used for shorter periods of time than their incandescent counterparts.
Often they use electronic ballasts. These contain small capacitors that can be used to smooth out the current and prevent RFI problems.
Most ballasts also incorporate fuses or fusable resistors in series with one side of the AC line. These help to prevent the fluorescent lamp from catching fire or melting down.
If there is a problem with the electric ballast, it is important to unplug the fixture before handling the parts. Otherwise, the ballast might burn up and be irreparably damaged by electric shock!
Some electronic ballasts have a pulsed DC output that can wear out the emissivity coating on the bulb’s filament more quickly than it does on the other end. This may cause the bulb to glow purple and then blacken, and eventually heat up.
This is a common condition on some older CFL’s that use an autotransformer and a.03 uF capacitor in series with the yellow filament winding. The resulting current flow causes the emissivity coating on one side of the tube to deteriorate faster than the other side and then it will start to glow purple and eventually blacken and heat up.
Once the emissivity coating on one end of the tube is gone, it will not be able to generate the ions needed for effective lighting and the lamp will fail. It’s best to replace the bulb with a new one before it fails completely.
There are many reasons for lamps to not light fully. This is why it is so important to have an electrician inspect a malfunctioning lamp and take a look at the wiring to see what the problem might be.
The most common reason for a lamp to not light fully is the failure of the ballast, but there are other possible causes as well. Some common ones are a bad ballast, cold lamps or a low ambient temperature, a reverse connected 120V ballast, and a defective lamp holder.
A poor ground connection can also be a problem, especially with fixtures that have a metal reflector. Most 4′ fluorescent fixtures (unlike compact fluorescents) are designed so that the “static electricity” leaks off to the metal frame and helps the lamp start by jumping the arc from one end of the tube to the other.